I find that varying the width of the sashing is the cure to a lot of evils (including panels that are not square and blocks that are not quite the same size).
One thing I do to make sure the 1/4" seam I use is the same on different machines is take a lined note card with me. The lines are 1/4" apart. I make sure I know where they are on my main machine, and I use it to set up the machine I take to class or DDs machine so I have a consistent size.